Viruses of the family Paramyxoviridae are enveloped negative-stranded RNA viruses which comprise two subfamilies, paramyxovirinae and Pneumoriniae. The subfamily Pararmyxovirinae includes Human Parainfluenza Viruses types 1, 2, 3 and 4, Mumps Virus, Newcastle Disease Virus, and Measles Virus. Human Respiratory Syncytial virus is a member of the subfamily Pneumovirinae.
As a group, these viruses are a leading cause of respiratory disease in humans, especially children. These paramyxoviruses are the causative agents of such respiratory diseases as croup, bronchitis, and pneumonia. Taken together the various stains of paramyxovirus are responsible for annual epidemics in humans. Re-infection in following years is common but less severe (Kass, ed., studies in Infectious Diseases Research, The University of Chicago Press, Chicago (1975), pp. 51-64). Although some immunity develops through infection by the various strains of paramyxoviruses it is not sufficient to provide complete protection. The vaccines that have been developed have been shown to have only limited efficacy in the short term so that long term usage is completely ineffective (Choppin and Schneid, Rev. Infect, Dis 2:40-61 (1980); Norrby et al., J. Infect Dis. 132:262-269 (1975). The lack of an effective vaccine together with the epidemiological evidence of the occurrence of annual epidemics of paramyxovirus infection indicates the urgent need for the development of therapeutic agents.